I came across this solution recently when I had to shrink tempdb. I tried shrinking each of the 8 data files plus CHECKPOINTs, repeatedly. It would not budge. I almost threw in the towel and emailed out that the space issue would be fixed during our next patching window, but then I found David Levy’s reply. DBCC FREEPROCCACHE worked like a charm.
Word of warning: understand what FREEPROCCACHE does before running it. In an emergency like the scenario Tara describes, the benefit outweighs the cost, but do be aware that there is a cost.